[Mp4-tech] [H.264] IPCM

[Tourapis, Alexis]

A simpler alternative would be to modify the function init_enc_mb_params() in mode_decision.c. You could then set the appropriate valid array entries to 0 (disabled), i.e. I8MB, I4MB, and I16MB, or 1 (enabled). You may also increase the probability of getting IPCM by disabling some intra mode directions using the following parameters :
Intra4x4ParDisable     = 1  # Disable Vertical & Horizontal 4x4	
Intra4x4DiagDisable    = 1  # Disable Diagonal 45degree 4x4
Intra4x4DirDisable     = 1  # Disable Other Diagonal 4x4
Intra16x16ParDisable   = 1  # Disable Vertical & Horizontal 16x16
Intra16x16PlaneDisable = 1  # Disable Planar 16x16
ChromaIntraDisable     = 1  # Disable Intra Chroma modes other than DC
The probability also increases depending on the QP you are using (lower QP means higher probability to get an IPCM mode). Finally, please note that it has been reported that there may still be issues with IPCM and CABAC. We have not yet tested why there are problems, but we will try fixing the problem in a future realease.
Best regards,
Alexis
-----Original Message-----
From: mp4-tech-bounces lists.mpegif.org [mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Dzung Hoang
Sent: Monday, January 15, 2024 9:21 AM
To: 'Sebastián López Suárez'; mp4-tech lists.mpegif.org
Subject: RE: [Mp4-tech] [H.264] IPCM 
Here are the steps to create a test image that forces IPCM.
1) Input a block of high-valued coefficients into the inverse 4x4 integer transform. Clip the output block to the range [0,255].
2) Create an image that replicates the block computed in step 1.
3) Encode the image.
The above recipe creates an input pattern that would require many bits to compress using the integer transform. The JM encoder would then be forced to use IPCM.
Regards,
- Dzung Hoang
-----Original Message-----
From: mp4-tech-bounces lists.mpegif.org
[mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Sebastián López Suárez
Sent: Monday, January 15, 2024 7:02 AM
To: mp4-tech lists.mpegif.org
Subject: [Mp4-tech] [H.264] IPCM 
Dear experts,
I am testing a propietary decoder and, within this process, I would like to verify if the decoder supports properly the decoding of IPCM. For that purpose I have generated several bitstreams with differents sequences and coding conditions, enabling for all the cases the use of IPCM mode (EnableIPCM = 1 at encoder.cfg). However, as the IPCM is an extremely unusual mode, in all the sequences the number of IPCM MBs was equal to zero.
Does anyone knows how to force the reference encoder to produce some IPCM macroblocks in a coded sequence? It can be made by simply modifying the configuration file? If not, which C files should be modified?
Thank in advance.
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